Loading GIF or, so called loader gif is an animation that indicates a loading process on a web-site or an application. Mostly the animations are used to show that something is loading on the background (e.g. AJAX applications). The animation objects are usually used in GIF format which is very popular due to it's history, but the loading images in SVG and CSS format are getting more and more poplular because of infinite size scalability - they can have any dimensions and relatively smaller size in bytes. There is also APNG (or animated PNG) format which appeared because of the GIF limitations, but was denied by a number of comminities in the beginning. At the moment the APNG format is supported by most major browsers now. It's still not very popular due to it's size in bytes comparing to all other formats.
Preloaders.net project provides more than 1000 different animations, split into 18 categories including most widely used loading spinners, horizontal bars, animated custom texts and others. Most of the non-3D images are available in 3 formats - GIF, APNG and SVG. For user convenience the images can be sorted to include only animations that are available in SVG format and by other options. Another subproject of ours provides the loading animations in CSS format.
But it's not the main functionality of the project. It's the generator form that allows users to modify the animated images as desired from within the web-site and create own unique "pre-loaders". Just click on a desired animation and you can set your own custom image colors, size, animation speed, frames amount and other advanced options. All loading icons on Preloaders.net project are free of charge both for personal and commercial use (except for re-distribution, which requires a reference to the project).
Most of the animations have the "add to cart" button. This button is there for users who are willing to purchase a source file (in Adobe Photoshop (.PSD) or 3DS Max (.MAX) format) for advanced use of the corresponding animation.